1. Field of the Invention
This invention relates to a material for converting an invisible ultraviolet ray into a visually observable visible ray with a high efficiency, and it is concerned with an oxide fluorescent glass capable of exhibiting visible fluorescence, which is useful for controlling an optical axis of a laser beam such as excimer laser and can be applied to fluorescent tubes for lamps, fluorescent fibers, backlights or display devices of LCD.
2. Description of the Prior Art
Phosphors using rare earth elements have widely been used up to the present time, mainly, as phosphors for lamps, color picture tubes, etc. Of late, materials for the anti-Stokes-wise wavelength conversion of infrared light into visible light have extensively been studied, for example, as to application to laser materials.
Tb ion showing a green fluorescence has been put to practical use as color picture tubes, high color rendering fluorescent lamps, etc. Eu ion showing a fluorescence with a narrow spctrum width in the red region has been put to practice as color picture tubes, high color rendering fluorescent lamps, etc. As described above, a phosphor using Tb or Eu has already been put to practical use, but such a phosphor is an opaque material which is obtained by coating a suitable carrier with a powdered phosphor to thus give only a superficial emission.
As such a glass utilizing fluorescence of Tb or Eu, there are used those described in Japanese Patent Publication Nos. 27047/1982 and 27048/1982 and Japanese Patent Laid-Open Publication No. 133780/1996.
However, the glasses described in these publications, for example, in Japanese Patent Publication No. 27047/1982 contain only at most 1.5 mol % of Eu.sub.2 O.sub.3 as a fluorescent agent. In the case of Japanese Patent Publication No. 27048/1982, only at most 1.5 mol % of Tb.sub.2 O.sub.3 is contained as a fluorescent agent. In such a degree of concentration of Eu.sub.2 O.sub.3 or Tb.sub.2 O.sub.3, no sufficient fluorescent intensity can be obtained. In the case of Japanese Patent laid-Open Publication No. 133780/1996, a large amount of a fluorescent agent is contained, but a fluorophosphate is used and thus, production of a glass for a fluorescent lamp or large-sized glass plate is difficult due to small thermal durability and small glass strength thereof.